Purpose: The purpose of this study was to evaluate the effect of nutrient rich and nutrient deficient growth media on pressure resistance of Escherichia coli K12 lux.
Methods: Escherichia coli K12 lux strains were grown in 100 ml nutrient rich Luria-Bertani broth and nutrient deficient M9 media, incubated for 16 hours at 37°C and sub-cultured in 100 ml fresh LB broth and M9 media until an OD600 ~0.5 was reached. A decanal solution was added to 1 ml culture for a 0.001% final concentration. Sample triplicates were contained in 350 μl polypropylene tubes and exposed to 50, 100 and 150 MPa over three 10 minutes compression and 10 minutes decompression cycles during which luciferase expression was recorded using a photomultiplier-tube directly connected to a sapphire window in the pressure vessel.
Results: Although Escherichia coli K12 lux grown in LB media showed slightly higher bioluminescence values than cells grown in M9 media, there was no significant effect of growth media on luciferase expression. Nevertheless, growth conditions had an effect (P < 0.05) on pressure induced bacterial inactivation, as cells grown in M9 media showed 0±0 log reductions for all pressure levels compared to 2±0 and 4±1 log reductions for 100 and 150 MPa for cells grown in LB media.
Significance: These findings suggest that prior exposure to nutrient deficient M9 growth media might have triggered a bacterial stress response that conferred cross protection against pressure. This needs to be considered for an effective and reliable use of this technology for food preservation.